How Battery Charging Time is Calculated
Charging time depends on the total Amp-hours needed, the maximum continuous current rating of your charger, and the chemical charging profile of the battery.
The 3 Stages of Battery Charging
- Bulk Phase (Constant Current): The charger pumps maximum rated current into the battery. Voltage rises steadily as the state-of-charge increases from 0% to approximately 80% (for lead-acid) or 95% (for lithium).
- Absorption Phase (Constant Voltage): The charger holds peak voltage (e.g. 14.4V for AGM or 14.2V for LiFePO4) while the internal resistance of the battery rises, causing current to taper down toward zero.
- Float Phase: The battery is fully charged; voltage drops to a maintenance level (13.6V – 13.8V) to compensate for self-discharge without overcharging.